An oscillator can produce clock signals and has widespread applications. In general, if a circuit comprises some basic sequential logic devices like a flip flop, the clock signal provided by the oscillator is needed to trigger the circuit. Conventional oscillators can be classified into a simple type of RC oscillators including transistors, resistors and capacitors, a type of voltage-controlled temperature-compensated crystal oscillators (VC-TCXO), or a type of voltage-controlled crystal oscillators (VCXO). The determination of using a specific type of the oscillators is usually made by judging the characteristics of the oscillator and the clock frequency that the circuit needs. Definitely, the oscillator needs power (electric energy) to work.
On the other hand, for most of portable electric products, such as laptops, personal digital assistants (PDAs) and mobile phones, batteries are usually the only power sources (i.e. power supplies). It is well known that the operation time of any battery is limited due to its material, volume and weight. Therefore, the portable electric products should promote the utilization rate of electric energy so as to reach the most effective exploitation upon the battery. Basically, the conception of saving electric energy is the same important not only for portable electric products but also for normal electric products. Such a trend can be seen from that most electric devices in the market have a so-called energy (power) saving mode to decrease the consumption of the power.
Usually, the designer always neglects the power consumption of the oscillator circuit who still works normally even the whole device has entered the power saving mode. Accordingly, to further implant the energy saving idea upon the oscillator, the present invention discloses a wake-up circuit to standby the oscillator if necessary.